A recent trend in the automotive industry is to enhance the specific power, i.e. the peak power per engine displacement liter. This is achieved through either multi-turbocharging or mechanical supercharging or external boosting, such as e-boosting which makes use of an electrically driven compressor. Further approaches involve more efficient turbochargers with both higher compressor and turbine efficiencies and lower inertia. An industry-wide trend is the use of downsizing, driven by fuel consumption reduction requirements. This places requirements for turbocharger components, which means that in order to produce more compressed air, the turbine may operate closer to its thermal limit.
The exhaust manifold temperature upstream of the turbine (this temperature is here and in the following denoted as “T3”) is an important parameter for modern diesel engine control. This temperature is used in particular for (i) turbo temperature protection (since a more accurate knowledge of T3 enables a closer control of the engine to the turbo limit and to extract more power from the engine), (ii) calculation of the EGR flow (since the orifice equation depends on the upstream EGR valve temperature), and (iii) prediction of the post turbo temperature used for aftertreatment modelling and OBD monitoring.
Conventional approaches involve a sensor for the pre-turbine temperature T3 in order to develop a limiting strategy. Typically, pre-turbine temperatures are limited to steady state limits of e.g. about 820-850° C. for diesel engines. For V-engines with separated exhaust manifolds, even two sensors can be necessary. However, since such temperature sensors are quite slow (with typical time constants of e.g. 1-2 s), a final steady state temperature measurement can take a significant amount of time of e.g. up to 10 s. Furthermore, although a large opening for the T3 sensor element gives a good response, soot and exhaust gases can reduce the accuracy and durability of such a sensor. Variations in exhaust conditions can have a further detrimental impact.
Furthermore, model-based turbocharger control is applied to complex, multi-stage or single stage turbocharger systems, which makes use not only of the compressor maps, but increasingly more of the turbine maps, such as pressure ratio versus corrected or reduced flow, but also turbine efficiency, for diagnostics, measures of performance degradation or increases in system performance, such as fuel economy. For such model-based calculations an accurate, dynamic T3 parameter is required.
Accordingly, the requirements for damage limitation, performance and model-based turbocharger control drive the demand for a fast, accurate T3 observer.
The inventors herein have recognized the above issues and provide a method and an observer for determining the exhaust manifold temperature upstream of the turbine in a turbocharged engine, which enables a sufficiently fast, accurate and robust determination of the exhaust manifold temperature with reduced effort and costs.
In one example, a method for determining an exhaust manifold temperature in a turbocharged engine, said engine including a turbocharger and a turbine and said exhaust manifold temperature including a temperature upstream of the turbine, said method comprises estimating a value of the exhaust manifold temperature based on a model, measuring a temperature downstream of the turbine, and correcting the value of the exhaust manifold temperature based on said measurement.
The disclosure involves the concept of constructing a fast and accurate T3 (=temperature upstream of the turbine) observer using a phenomenological/combustion-based T3 model, wherein the observer is robustified using a measurement of the temperature T4 (=temperature downstream of the turbine) and, as further described in the following, optionally a measurement or estimation of the turbocharger speed. The disclosure is also based on the concept to estimate the exhaust manifold temperature while avoiding the costs of an additional sensor. The disclosure presents a method to infer the exhaust manifold temperature from a model with correction from a downstream sensor which is required anyway, thus saving the cost of at least one sensor.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.